Louis-Marie writes:

> I also have a remark about backuppc pooling feature: I think the server
> locally detects file duplicates by hashing them after download. As far
> as I know, rsync should also be able to send some kind of hash from
> remote host before download. Wouldn't it be possible to detect
> duplicates using this hash before the file is downloaded? This would for
> example save downloading files again when a user simply renames a
> directory...

Rsync only efficiently transfers changes to files that have the same
path.  Rsync does not detect renamed files - it does a complete transfer
in that case.  (Some work was done patching rsync to do "fuzzy" matching
to try to find some renamed files.)  BackupPC uses the efficiency of
rsync transfers, and then globally matches identical files.  A renamed
file will be verbatim transferred and then matched to the pool.

If the rsync transfer determines the file is identical, BackupPC
simply adds a hardlink.  If the rsync transfer notices even a small
change to a file, just the change will be transferred, but then
BackupPC needs to reconstruct the full file to determined whether
a match is in the pool.

Craig

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